Recently, in dialysis apparatus used as a blood purification apparatus, a technique has been suggested that performs priming, reinfusion, and substitution (emergency substitution) using a dialysate to be supplied to a dialyzer during dialysis treatment (particularly, an on-line HDF or an on-line HF). For example, Japanese Laid-open Patent Application No. 2004-313522 discloses a dialysis apparatus that includes a substitution line that has one end connected to a collection port formed in a predetermined part of a dialysate introduction line. The other end is connected to a blood circuit (arterial blood circuit or venous blood circuit). A substitution pump is disposed in the substitution line. In order to perform the priming, the reinfusion or the substitution (the emergency substitution) using the dialysis apparatus, the dialysate in a dialysate introduction line is supplied to the blood circuit (the arterial blood circuit or the venous blood circuit) by driving the substitution pump.
However, in a blood purifier (hereinafter, called an on-line HDF) that is applied to the blood dialysis filtration (HDF) and uses the dialysate as the substitution, there is a need to perform the substitution (including a pre-substitution performing substitution by the arterial blood circuit, and a post-substitution performing substitution by the venous blood circuit) of the dialysate to the patient's blood by ultrafiltration corresponding to a filtration treatment as the HDF treatment. As an apparatus applied to the on-line HDF, as disclosed in Japanese Laid-open Patent Application No. 2001-112863, a dialysis apparatus has been suggested that has a dialyzer, a blood circuit constituted by an arterial blood circuit and a venous blood circuit with a blood pump. A dialysate introduction line introduces the dialysate into the dialyzer. A dialysate discharging line discharges the dialysate from the dialyzer. A substitution line (a pre-substitution line or a post-substitution line) supplies the dialysate of the dialysate introduction line to the blood circuit to perform the substitution without going through the dialyzer.
In the dialysis apparatus that has the pre-substitution line, which is able to perform the pre-substitution, and since the patient's blood circulating extracorporeally is subjected to the substitution before reaching the dialyzer, in the dialyzer, the blood diluted by the substitution is filtrated. Thus, in general, the dialysis apparatus performing the pre-substitution can drive the substitution pump more rapidly than devices that perform post-substitution. Thus, it can sufficiently perform the dilution using the substitution.
However, in the blood purification apparatus performing the pre-substitution of the related art described above, problems exist. Just after the blood purification is started, or just after the driving is started after stopping the substitution pump once, the dialysate, as the substitution, is not supplied to a channel (hereinafter, such a part is called a “dilution channel section”) in the arterial blood circuit. Thus, sufficient dialysate is not supplied, the dilution is insufficient, and the blood, with high concentration, flows between a connection part to the substitution line in the arterial blood circuit and the dialyzer.
Meanwhile, a predetermined amount of dialysate, as the substitution, is supplied to the arterial blood circuit from the dialysate introduction line. A flow rate of the dialysate introduced into the dialyzer is reduced by the flow rate supplied as the substitution that the dialysate discharged from the dialyzer. Thus, even if there is no driving of the ultrafiltration pump or the like, filtration is performed using the dialyzer. As a result, there has been a concern that the blood with insufficient dilution may be further filtrated. Thus, there is a problem that the blood circulating extracorporeally is excessively concentrated. Furthermore, as described above, the fluid purification apparatus performing the pre-substitution is configured so as to drive the substitution pump faster than a case of performing the post-substitution. Thus, there is a disadvantage that the excessive concentration is easily generated.